In oil well drilling equipment the coupling and uncoupling, or so-called "making" and "breaking" of the connection on tubular is usually effected by pipe gripping tongs. The lower pipe section is usually gripped and held against rotation by a "back-up" tong and the upper pipe section is usually gripped and rotated by an upper "break-out" or "make-up" tong.
A variety of mechanical arrangements have been employed to advance the jaws within a back-up tong in order for such jaws to engage with and grasp the tubular. In U.S. Pat. No. 4,647,777 three jaws are advanced radially inwardly along linear paths by the direct application of hydraulic pressure to the jaws. In U.S. Pat. No. 4,402,239 a pair of opposed jaws are advanced radially inwardly by hinged linkages connected to a hydraulic cylinder. In U.S. Pat. No. 4,778,742 the jaws are carried on hinged supports and are driven inwardly along arcuate paths by the rotation of the supports under hydraulic pressure. Lastly, in U.S. Pat. No. 4,290,304 a pair of opposed jaws are driven radially inwardly by the rotational advancement of a crescent-shaped wedge carried on a "C"-shaped ring that is turned through gearing linked to a hydraulic motor.
In all of the above cases the mechanical systems transmit a force to the jaws that is dependent on the position and shape of the parts, following a single, fixed force-application schedule. While pipe of slight variations in diameter may be accommodated without a change of parts, if pipe of substantially different diameter is to be grasped, major parts must be changed to adjust the schedule by which the force is applied. This is a separate consideration from that of using interchangeable jaws to provide grasping surfaces that accommodate pipes of differing diameters.
It is an object of this invention to provide a mechanical layout for tongs that accommodates the use of a wedge or combination of wedges to place a gripping apparatus about a tubular surface and apply a gripping force thereto. The ready inter-changeability not only of jaws but also of intermediate components that govern the schedule by which force is applied to pipe with the advance of the jaws within a tong render the invention convenient and advantageous.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.